Tuning of interfacial charge transport in polyporphine/phthalocyanine heterojunctions by molecular geometry control for an efficient gas sensor

Abstract

Owing to high interfacial conductivity, organic heterostructures hold great promises to augment the electrical performances of electronic devices. In this endeavor, the present work reports fabrication of novel polyporphine/phthalocyanine heterostructures and investigates the modulation of charge transport induced by structural change of polyporphine and its implication on ammonia sensing properties. Polyporphines materials are electrosynthesized by oxidation of zinc(II) porphine monomer that corresponds to the fully unsubstituted porphyrin. At less-positive anodic potential, low conducting meso,meso-singlylinked type-1 polymer (pZnP-1) is formed in which a monomer unit stays orthogonal to its neighbors. At higher anodic potential, monomer units are fused in the 2D plane to produce β,β-meso-meso-β,β-triply-fused type-2 polymer (pZnP-2), having a π-conjugated structure and high conductivity. Association of these polymers in organic heterojunction devices with lutetium bis-phthalocyanine (LuPc 2 ) reveals non-linear current-voltage (I-V) characteristics typical for interfacial accumulation of charges in the heterostructure for pZnP-1 and a linear I-V behavior for pZnP-2. Characterization of these heterojunctions by impedance spectroscopy further confirms the predominance of interfacial charge transport in pZnP-1/LuPc 2 which is improved with increasing bias, while largely bulk charge transport independent of bias prevails in pZnP-2/LuPc 2 device. Different regimes of charge transport influence ammoniasensing properties of the devices, such that pZnP-1/LuPc 2 demonstrates highly sensitive, reversible and stable response, while pZnP-2/LuPc 2 shows low and unstable response.

Molecular Engineering of Silicon Phthalocyanine to Improve the Charge Transport and Ammonia Sensing Properties of Organic Heterojunction Gas Sensors

“…[18] As a consequence, sensor performance toward NH 3 gas demonstrated an improvement in sensitivity, reproducibility, response/recovery kinetics, and operational stability compared to existing chemiresistors. [19,20] A wide range of molecular semiconductors and polymers have been investigated as active sensing materials in organic heterojunction sensors for NH 3 detection including metal phthalocyanines (MPc), polyporphyrins, [21,22] perylene derivatives, [23] and triphenodioxazine. [24] MPcs are thermally stable conjugated macrocycles with favorable semiconducting properties making them ideal for use in organic heterojunction sensors, besides other areas of organic electronics such as organic thin-film transistors (OTFTs) and organic photovoltaics (OPVs).…”

Highly Sensitive and Selective Organic Gas Sensors Based on Nitrided ZSM-5 Zeolite

“…We investigated the NO 2 gas-sensing performances of OFET gas sensors based on the P3HT/zeolite blend films with different degrees of nitridation. − The gas-sensing performances were measured in the linear region, at a fixed V D of −10 V and a fixed V G of −10 V. Figure d,e shows the changes in the normalized source–drain current [ I D ( t )/ I D (0)] when the fabricated gas sensors were repeatedly exposed to 10 ppm of NO 2 for 20 s and purged with air for 200 s. The P3HT film with 30 wt % of OZ exhibited the greatest increase in drain current compared to the homo-P3HT film and P3HT films with different amounts of OZ (Figures d and S3). The P3HT film with 50 wt % of OZ showed poor responsivity toward NO 2 gas, which indicates that the aggregation of zeolites interrupts the efficient approach of gas molecules toward the active layer.…”

Discrimination and detection of NO2, NH3 and H2S using sensor array based on three ambipolar sandwich tetradiazepinoporphyrazinato/phthalocyaninato europium double-decker complexes

“…As is already known, active sensing semiconductor materials, 3 the optimized microstructure of the active layers 4,5 and advanced device preparation 6,7 usually achieve a good sensing performance with a high sensitivity and selectivity. Among the sensing semiconductor materials, the sandwichtype phthalocyanine family has attracted extensively research interest because of the excellent charge transport properties, easy modulation of the frontier molecular orbital energy levels, and quite good solubility in common organic solvents [8][9][10][11] which allow low-cost and large-area devices to be fabricated by solution-based methods such as spin coating, 12 molecular assemblies, 13 Langmuir, 14,15 and quasi-Langmuir-Sha ¨fer (QLS) techniques, 16 and so on.…”